Milling cutter

ABSTRACT

A milling cutter composed of various disks joined together to form a unit is proposed. A tool disk  11  is fixedly joined to at least one supporting disk  12  at the side by soldering, gluing or welding. The inside diameter of the bore  15  of the tool disk  11  corresponds at least to the inside diameter of the bore  16  of the supporting disk  12.

[0001] The present invention relates to a milling cutter according to the preamble of Patent Claim 1.

[0002] Milling machines are usually used for cleaning, roughening and/or abrading concrete, asphalt or metal surfaces. They are also used to remove rubber from airport runways, roadway markings and floor coverings. The milling tool is a rotating cage-like milling drum. Built like a thread bobbin, it has at least two carrier shafts running parallel to the core on its circumference, where several freely rotating milling wheels are arranged. A typical milling machine is disclosed in European Patent 0 661 144. The design of the tool holder of a milling tool whose carrier shafts (which are subject to wear) can be replaced is disclosed in German Utility Model 298 22 034, for example.

[0003] Originally milling cutters resembling gearwheels made of a tough hardened steel were used as tools on these carrier shafts. To increase the stability under load of the elevations (beater heads) striking the surface to be machined at the largest circumference of such milling cutters, hard metal pins have been pressed into the head, at least to two-thirds of their length being pressed into and/or soldered in holes prepared for them. This method of producing such milling cutters is extremely expensive. In addition, these designs have the disadvantage that the pins pressed into and soldered in the head may be knocked out during use, which of course results in extremely rapid overall wear on such a milling cutter.

[0004] In recent years, milling cutters made entirely of hard metal have been used to an ever-increasing extent. This eliminates the labor-intensive and therefore expensive soldering of hard metal pins. Production of hard metal parts is relatively advantageous today, milling cutters made of hard metal are effective in use and thus higher output can be achieved depending on the surface properties, so this is also suggested as a relatively inexpensive option.

[0005] In the choice of the grade of material used for the milling cutters, the toughness, hardness, wear resistance and brittleness properties should be taken into account. Extremely hard material is very effective in use, but it is too brittle and does not have good wear resistance because pieces easily chip away from the mass. Conversely, a wear-resistant material is not brittle, i.e., no pieces chip away from the mass in this case, but it is not as effective in use. A compromise is sought in order to achieve the greatest possible toughness. These properties are determined by the ratio of tungsten to cobalt in the production of hard metal. Hard metal alloys that can be used economically are usually brittle.

[0006] Milling tools produce the desired abrasion by the fact that the milling cutters are held by centrifugal force on the outside of the circumference of the rotational movement and then strike the surface to be machined with a greater force and abrade material there. The milling cutter is not damaged too greatly because through the striking action itself, a rotational movement of the milling cutter on the carrier shaft is induced. When used on hard metal wheels, this often means that individual fragments may be chipped away from the milling cutter and flung outward by the centrifugal force, thus presenting a hazard for anyone in the vicinity. In the worst case, a milling cutter may break apart entirely. This poses a high accident risk for the operating personnel. The question of product liability also plays an important role for a manufacturer. This is the reason why the manufacturers of such tools recommend the use of milling cutters made entirely of hard metal only for the final fine machining of a surface.

[0007] The same milling cutters made entirely of hard metal, however, also tend to be chipped away at the center, i.e., where they move freely on the carrier shaft of the tool holder (drum). The diameter of the bore of the milling cutter is somewhat larger than the outside diameter of the carrier shaft. At the side the milling cutters are guided mutually with a large play and through washers and spacers which are provided between them and rapidly become worn away. The lateral play of the milling cutter on the carrier shaft thus becomes greater, the lateral guidance becomes worse and due to the greater freedom of mobility of the milling cutters, the forces leading to wear are increased. A rotational movement of the milling cutters on the carrier shaft is induced by the impact acting on them in abrasion on the surface machined. Normally the force created by this impact does not act exactly radially in the direction of circumferential movement of the milling tool. This results in forces which do not act radially to the milling tool and, which is worse, do not act at a right angle to the axis of the milling tool and the carrier shaft. If the surface to be machined is not struck radially to the milling tool and perpendicularly to the carrier shaft, then the milling cutter will strike the carrier shaft with an edge of the bore. This is what causes pieces to be chipped away. In another use of this milling cutter, the location chipped away on the carrier shaft acts like a milling tool or a cutting tool and therefore significantly reduces the service life of the carrier shaft. Such beating milling cutters with too much play on the carrier shaft result in irregular abrasion of the surface to be machined and must be replaced.

[0008] The object of the present invention is to improve upon a milling cutter of the type defined in the preamble such that the bore of the milling cutter is protected from pieces being chipped away from its edges, the outside contours of the milling cutter which yields the best results for surface machining with regard toughness hardness and effect.

[0009] This object is achieved by a milling cutter for a rotary cutting machine having the features of Patent Claim 1. Additional features according to this invention are derived from the dependent claims and their advantages are explained in the following description.

[0010] The drawing shows:

[0011]FIG. 1 a view of the milling cutter;

[0012]FIG. 2 a view of the milling cutter with pins;

[0013]FIG. 3 a view of the milling cutter with cutting blades;

[0014]FIG. 4 a view of the milling cutter with points and prongs;

[0015]FIG. 5 a section through a milling cutter;

[0016]FIG. 6 a section through a milling tool.

[0017] The figures show preferred embodiments which are explained in the following description.

[0018] A milling cutter 10 is described, consisting of various disks 11, 12. At least one tool disk 11 is joined at its end faces to one supporting disk 12 on one side or to two supporting disks 12, 12′, one on each side, by soldering, gluing or welding.

[0019] A milling tool consists of a tool holder 1 (FIG. 6) on whose circumference are mounted carrier shafts 3 on which a number of milling cutters 10 are mounted. Care is taken to be sure that the number of milling cutters 10 and spacers 13 is selected so that the extent in the axial direction of the carrier shaft 3 from the milling cutters 10 and spacer disks 13 still allows both to rotate on the carrier shaft 3, but to have as little lateral play as possible. Over a period of use, this play becomes greater due to the wear on the end faces of all the mounted parts.

[0020] If the milling cutter 10 consists of only one tool disk 11 and one supporting disk 12, the play between the milling cutters 10 and spacers 13 must not be too great, so that lateral guidance can be guaranteed. Therefore, in practice a tool disk 11 is always connected to a supporting disk 12 at both end faces so that milling cutter 10 is not out of balance in rotation about the carrier shaft 3 and does not become free merely due to the lateral forces. Such forces would promote wear on the end face. The design is advantageously symmetrical, as illustrated in FIG. 5, for example.

[0021] Each tool disk 11 is provided with so-called beater heads 20 on its circumference. Although the basic mass of the tool disk provides the necessary mass, work is performed with these beater heads 20. By rotation of tool holder 1, the milling cutters 11 are thrown outward by the centrifugal force on their carrier shafts 3 as illustrated in FIG. 6. The diameters of the bores 15 of the tool disks 11 and bores 16 of the supporting disks are always larger by a few millimeters than the outside diameter of the carrier shaft 3. In contrast with that, the diameter of bore 17 of spacer disks 13 is kept within a dimension similar to the diameter of carrier shaft 3 so that they sit with little play on the carrier shafts.

[0022] When tool holder 1 rotates about the axis A, it is lowered slowly onto the surface to be machined. A device illustrating this procedure is presented in European Patent 0 661 144. When milling cutters 10 with beater heads 20 strike the surface to be machined, a sudden rotation about carrier shaft 3 is induced. Since beater heads 20 are fixedly connected to milling cutter 10, the entire mass of supporting disk 12, tool disks 11 and beater heads 20—in short, the entire milling cutter 10—must be set in motion in this operation. This takes place according to the principles of the law of momentum, so that the beater heads 20 set the surface in rotation with a force which corresponds to the momentum which is to be expended and is necessary to induce rotation of this milling cutter 10. A surface is machined in this way.

[0023] A conventional milling cutter today is illustrated in FIG. 1. The tool disk 11 is made of a tough resistant steel, and the beater heads 20, which are subject to a great deal of abrasion, are made of hard metal. Bores 30 have been inserted into the tool disks 11 on the outside diameter as illustrated in FIG. 2. Hard metal pins 21 are inserted into these bores and in many cases are further secured by soldering. Milling cutters 10 constructed in this way are inserted into the body. Their problems include a poor service life, which is limited due to the loss of pins 21 that are knocked out during use, and the labor-intensive production of such milling cutters, as illustrated in FIGS. 1 and 2. Attempts to manufacture milling cutters 10 by the methods conventionally used in the machine industry have been unsuccessful. Hard metal cutting blades which are only soldered on without being securely anchored in the material of the tool carrier 11 do not have a secure enough hold and are knocked out in the first use. A reasonable service life is achieved only with pins 21, whose greatest length is anchored in bore 30.

[0024] The idea now is to manufacture milling cutters 10 entirely of hard metal. They may be designed like a tool disk 11 in FIG. 1 with beater heads 20 in the form of cutting blades 22 (FIG. 3), teeth 23 or prongs 24 (FIG. 4) designed on their outside diameter. Tool disks 11 designed in this way are customary in the industry. However, the service life of the carrier shafts 3 manufactured of a softer material is diminished when using such milling cutters 10 made entirely of hard metal. Such milling cutters 10 are also very expensive.

[0025] The idea on which this invention is based is to securely connect the tool disk 11 made of hard metal to supporting disks 12 at the side so that the tool disk 11 forms a unit 12/11/12′ with the supporting disks 12 that are fixedly secured at the side (FIG. 5). Supporting disks 12 act like reinforcements in such a design. The amount of hard metal may be reduced because the tool disk 11 may be designed to be thinner. In the choice of the grade of hard metal used, it is possible to decide freely because the tool disk 11 need not have such a great inherent strength. It is supported by supporting disks 12, 12′.

[0026] To provide unit 12/11/12′ with a good inherent strength, the three disks are joined by welding, soldering, screwing or riveting them together. This unit 12/11/12′ should be supported on the carrier shaft 3 as broadly as possible. Only the supporting disks 12, 12′ should be in contact with the carrier shaft 3. Therefore, the diameter of bore 16 of the supporting disks 12 will always be equal to or less than the diameter of bore 15 of tool disk 11. This in turn results in the bore 15 of the tool disk 11 not being chipped away and the unavoidable impacts acting on the carrier shaft 3 in the use of milling cutter 10 are distributed over a larger area or a greater length 1 (FIG. 5). 

1. A milling cutter composed of various disks combined to form a unit, characterized in that at least one tool disk (11) is fixedly joined to at least one supporting disk (12) at the side by soldering, gluing or welding, whereby the inside diameter of the bore (15) of the tool disk (11) corresponds at least to the inside diameter of the bore (16) of the supporting disk (12).
 2. The milling cutter according to claim 1, characterized in that the tool disk (11) has beater heads (20) on its circumference.
 3. The milling cutter according to claim 2, characterized in that the beater heads (20) are pins (21) which are pressed into and soldered in bores (30) provided for this purpose in the tool disk (11), the pins (21) being made of hard metal and the tool disk (11) being made of steel.
 4. The milling cutter according to claim 2, characterized in that the beater heads (20) are designed in the form of cutting blades (22).
 5. The milling cutter according to claim 2, characterized in that the beater heads (20) are designed in the form of points (23).
 6. The milling cutter according to claim 2, characterized in that the beater heads (20) are designed like prongs (24).
 7. The milling cutter according to claims 1 and 2, characterized in that the tool disk (11) is made of hard metal and the supporting disks (12) are made of high-strength steel. 